The present invention relates to an erect image, unity magnification, resin lens array and to a method for manufacturing the same. More particularly, the invention relates to an erect image, unity magnification, resin lens array applicable to a device for spatially transmitting a two-dimensional image and a method for manufacturing the lens array, as well as to a method for manufacturing a mold for use in manufacture of the lens array.
An erect image, unity magnification lens array used in a copier, facsimile, or printer is disclosed in Japanese Patent Application Laid-Open No. 55-90908. The publication proposes a two-block lens array in which each block includes a number of bar lenslets and the two blocks are arranged so as to face each other. Such a lens array is formed by the steps of, for example, covering with an acrylic resin a lens support in which through holes are bored at positions corresponding to intended bar lenslets; and pressing dies having hemispherical concaves formed therein against the acrylic resin assembly from the opposite side to thereby form end faces of bar lenslets.
Japanese Patent Application Laid-Open No. 64-88502 discloses a lens array including two flat lenses which face each other. Each flat lens is formed by injection molding such that convex lenslets are arrayed in a two-dimensional regular pattern.
FIG. 8 of Japanese Patent Application Laid-Open No. 60-29703 depicts a usually practiced method for manufacturing a microlens array. According to the method, a polymer is deposited on a mold having concaves formed therein in an array, thereby forming the microlens array.
Japanese Patent Application Laid-Open No. 5-150102 discloses a method for manufacturing a microlens array, comprising the steps of: forming a mask layer on a flat plate; forming fine circular openings at intended lenslet positions in the mask layer, in a number equal to the number of intended lenslets; chemically etching the surface of the flat plate through the openings; removing the mask layer; further chemically etching the surface of the flat plate to obtain a mother matrix; fabricating a mold for use in molding a microlens array, by use of the mother matrix; and pressing a glass sheet against the mold (the so-called xe2x80x9c2P molding processxe2x80x9d), thereby fabricating a microlens array on which convex lenslets are densely formed on one side.
An ordinary resin lens array is intended to converge luminous flux on each of arrayed targets. Accordingly, the accuracy of lenslet pitches must be equivalent to the positional accuracy of the targets. To this end, the resin lens array must be manufactured by the 2P molding process.
An erect image, unity magnification, resin lens array is applicable not only to a copier, facsimile, or printer but also to a two-dimensional image, spatial transmitting device for transmitting a two-dimensional image onto a spatial image plane. A specific example of such a transmitting device is a touchless switch. An erect image, unity magnification, resin lens array for use in such a two-dimensional image, spatial transmitting device is not required to have a high degree of lenslet pitch accuracy so long as the optical axes of at least three stacked hemispherical lenslets are aligned.
The inventors of the present invention carried out extensive studies in an attempt to manufacture an erect image, unity magnification, resin lens array by injection molding, not by a 2P molding process.
An erect image, unity magnification, resin lens array which the present inventors aim to provide includes at least two lens plates, which each have hemispherical lenslets of 0.2 mm to 2.0 mm diameter arrayed in a regular pattern on one or both sides thereof. The lens plates are stacked such that the optical axes of at least three stacked hemispherical lenslets are aligned. The working distance of the intended lens array is not greater than 100 mm. Accordingly, the stacked hemispherical lenslets of the lens plates have a common optical axis, and the common optical axes are in parallel to each other.
As mentioned previously, Japanese Patent Application Laid-Open No. 64-88502 describes that a flat lens array is manufactured by injection molding, but the publication does not disclose a specific procedure therefor. According to Japanese Patent Application Laid-Open No. 5-150102, a Ni mold for use in fabrication of a microlens array is manufactured. However, this Ni mold is not applicable to injection molding which the present inventors aim to provide. In the case where a glass mother matrix is fabricated, if a pinhole is present in a chromium film, glass is etched through the pinhole, resulting in formation of an undesirable pit in the glass mother matrix. As a result, a mold fabricated by use of the glass mother matrix involves a defect.
Further, when a lens plate is manufactured by injection molding, the injection-molded lens plate is warped and suffers molding shrinkage. Therefore, when the warped, shrunk lens plates are assembled into an erect image, unity magnification, resin lens array, there must be devised a measure for rendering the lens array free of distortion.
An object of the present invention is to provide a method for manufacturing an erect image, unity magnification, resin lens array by injection molding through use of a defect-free mold.
Another object of the present invention is to provide an erect image, unity magnification, resin lens array manufactured by the method of the invention.
Still another object of the present invention is to provide a lens plate for use in the aforementioned erect image, unity magnification, resin lens array and a method for manufacturing the lens plate by injection molding.
A further object of the present invention is to provide a mold for use in the aforementioned injection molding and a method for manufacturing the mold.
A still further object of the present invention is to provide a mother matrix for use in manufacture of the aforementioned mold and a method for manufacturing the mother matrix.
A still further object of the present invention is to provide a master matrix for use in manufacture of the aforementioned mother matrix and a method for manufacturing the master matrix.
The erect image, unity magnification, resin lens array of the present invention includes lens plates which each have hemispherical lenslets arrayed in a regular pattern. According to the method of the invention for manufacturing the resin lens array, first there is manufactured a master matrix for a mold for use in injection-molding of the lens plate. The master matrix is manufactured by the steps of: preparing a glass substrate having substantially parallel, flat surfaces; forming an etching resist film on the glass substrate; patterning the etching resist film so as to form fine openings corresponding to the hemispherical lenslets in the etching resist film in a regularly arrayed pattern; isotropically etching the glass substrate while using the patterned etching resist film as a mask, thereby forming concaves in the glass substrate under the corresponding fine openings; removing the patterned etching resist film; further isotropically etching the glass substrate so that the concaves grow and assume a profile corresponding to that of the hemispherical lenslet.
By use of the thus-manufactured master matrix, the mold for use in injection molding is manufactured. A method for manufacturing the mold includes the steps of: applying a parting agent onto the surface of the master matrix on which the concaves are formed; drying the applied parting agent; dropping resin onto the surface of the master matrix; spreading the dropped resin by use of a glass substrate; curing the spread resin; parting the master matrix from an assembly of the cured resin and the glass substrate; forming a conductive film on the surface of the cured resin of the assembly; depositing metal on the conductive film to a predetermined thickness by plating; and parting the resultant metal plating from the assembly to thereby obtain the mold.
Next, a lens plate is manufactured by use of the thus-obtained molds. A method for manufacturing the lens plate includes the steps of: attaching two molds onto a die set such that surfaces having concaves formed therein face each other; establishing a predetermined gap between the facing molds; injecting resin into the gap; and opening the molds apart to remove the lens plate.
Subsequently, the thus-obtained lens plates are assembled into an erect image, unity magnification, resin lens array. The assembling method includes the steps of: stacking two lens plates, which are convexly warped, such that convexly warped sides thereof face each other or face in the same direction while directions of resin injection thereof are aligned; and clipping the lens plates together at clipping portions thereof.